1. Field of the Invention
The present invention relates to a device and method for dynamically controlling the formation of stitches in a sewing device.
2. Description of Related Art
Embroidery stitching requires appropriate stitch tension control. Prior art sewing and embroidery machines use a static control means for controlling the formation of stitches. More specifically, the amount of up/down movement of the needle was fixed and constant (i.e., fixed stitch cycle). This relies on the thread source (e.g., the spool) to hold back all thread feed except that needed for the particular stitch.
In addition, the movement, in the horizontal plane, of the workpiece being stitched itself acted to pull the thread from the spool of the machine so that each subsequent stitch could be made. This drag tensioning in the source of the thread has been used with both lock-stitch and single thread techniques. With prior single thread embroidery techniques, the drag tension is provided by pulling against the previous stitch made in the workpiece.
In the above instance, the dynamic force loads created by the dynamic thread feed requirements throughout the stitch cycle cause variable pulling forces on the thread. These forces are shared by the feed drag mechanism and the holding friction of the anchoring of the previous stitch. The static force of prior art drag mechanisms result in uncontrolled shared pull of the thread from the feed spool and previous stitch.
The variable thread feed requirements of short and long stitches results in uneven tensioning. With such a variable thread tension, it is difficult to ensure proper tension in the thread stitches. Thus, the quality of the stitches made may be adversely affected. In addition, this variable thread tension can result in thread slippage at the point where the thread feeding device engages with the thread to pull the thread from the spool.
The above problems associated with typical control of thread feeding have a particularly negative impact at fast stitching speeds. These problems particularly present themselves when using an alternative to conventional lockstitch embroidery, which employs a replaceable cartridge containing a needle and embroidery thread, supplied pre-threaded by means of a hollow needle of the type commonly used for intravenous injection. A stitching mechanism creates underside loops retained in the workpiece by friction (so called “single-needle” embroidery or stitching). Since the stitches in single-needle embroidery are not locked at the underside of the workpiece by another portion of thread, the uneven tensioning associated with typical stitching control often pulls too hard against one of the unsecured stitches causing the stitch to come undone.
Prior art machines of this type have the capacity to install only a single cartridge at one time, such that an embroidery pattern of several colors requires several cartridge changes performed by the user, interrupting an otherwise automated process. Embroidery patterns commonly comprise eight or more colors, resulting in a tedious operation to produce a single finished workpiece.